web/vtctld: Add messages for empty shard/tablet lists.

web/vtctld/keyspaces.html

@@ -27,7 +27,7 @@
 
 	<md-card-content>
 
-	<h3>Shards</h3>
+	<h3 ng-bind="keyspace.shards.length == 0 ? 'No shards found.' : 'Shards'"></h3>
 
   <md-grid-list md-cols-sm="2" md-cols-md="4" md-cols-gt-md="8"
       md-row-height="2:1" md-gutter="1em">

web/vtctld/shard.html

@@ -29,6 +29,10 @@
 <md-card>
 <md-toolbar><div class="md-toolbar-tools"><h2>Tablets (by cell)</h2></div></md-toolbar>
 
+<md-content ng-if="cells.length == 0" class="md-padding">
+  <h3>No tablets found.</h3>
+</md-content>
+
 <md-tabs md-border-bottom md-dynamic-height md-center-tabs="false" ng-if="cells.length">
 <md-tab ng-repeat="cell in cells" label="{{cell.name}}" md-on-select="setSelectedCell(cell)">
 <md-content class="md-padding" layout="row" layout-wrap>